The present invention relates to a booster which is used in a brake of automobile or the like, and more particularly, to an improvement of a reaction transmission mechanism.
A booster is known in the art comprising a tubular valve body slidably disposed within a shell, a valve plunger slidably fitted into the valve body and coupled to an input shaft for movement therewith, an output shaft having a rear end which is slidably disposed within the valve body, and a reaction disc disposed between the end of the output shaft and the valve plunger for transmitting a reaction from an output acting upon the output shaft to the valve plunger, the arrangement being such that in the inoperative condition where the input shaft is not driven forward, a clearance is maintained between the reaction disc and the valve plunger.
In the conventional booster arranged in the manner mentioned above, in the operative condition where the input shaft is driven forward, the valve plunger abuts against the reaction disc, whereby a reaction from the output acting upon the output shaft is transmitted to the input shaft through the reaction disc and the valve plunger.
However, with a conventional booster as mentioned above, it is desired to have an increased hysteresis for an input in order to afford a favorable brake feeling to a driver. In addition, it is desired to increase the magnitude of the hysteresis in a greater output operating region in comparison to the magnitude of the hysteresis in a lower output operating region.
The magnitude of the hysteresis can be increased by increasing the hardness of the reaction disc of the conventional booster as mentioned above, for example.
However, when the reaction disc has an increased hardness, there results a disadvantage that a variation in the jumping value as the booster is operated or in the servo ratio increases.
In view of the foregoing, it is an object of the invention to increase the hysteresis with a simple arrangement without increasing the hardness of the reaction disc.
In accordance with the invention, the booster mentioned above further comprises resistive means which applies a resistance to the retracting movement of the valve plunger relative to the valve body in accordance with the reaction which is transmitted from the reaction disc to the valve plunger when the booster is operative where the input shaft is driven forward.
With this arrangement, in the operative condition where the input shaft is driven forward, the valve plunger retracts toward its inoperative position as an input or a force with which a brake pedal is depressed is reduced, but the resistive means applies a resistance to the retracting movement of the valve plunger in the rearward direction. Accordingly, the magnitude of a hysteresis, which represents a difference between inputs which provide an equal output as the brake pedal is depressed and released can be increased.
The resistance applied to the valve plunger is greater in a higher output operating user than in a lower output operating region.
Accordingly, the magnitude of the hysteresis can be increased without increasing the hardness of the reaction disc.
Above and other objects, features and advantages of the invention will become apparent from the following description of several embodiments thereof with reference to the attached drawings.